As the commercially available antitumor agents of pyrimidine series metabolism antagonistic agents, 5-fluorouracil (Duschinsky, R., et al., J. Am. Chem. Soc., 79, 4559 (1957)), Tegafur (Hiller, SA., et al., Dokl. Akad. Nauk USSR, 176, 332 (1967)), UFT (Fujii, S., et al., Gann, 69, 763 (1978)), Carmofur (Hoshi, A., et al., Gann, 67, 725 (1976)), Doxyfluridine (Cook, A. F., et al., J. Med. Chem., 22, 1330 (1979)), Cytarabine (Evance, J. S., et al., Proc. Soc. Exp. Bio. Med., 106, 350 (1961)), Ancytabine (Hoshi, A., et al., Gann, 63, 353, (1972)), Enocytabine (Aoshima, M., et al., Cancer Res., 36, 2726 (1976)), etc. are so far known.
As the pyrimidine mononucleoside having a cyano group at the ribose moiety, 3'-cyanothymine nucleoside and 3'-cyanouracil nucleoside derivatives are only known (Japanese Unexamined Patent Publication Nos. Hei-2-83392, Hei-2-104586 and Hei-2-503002).